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How does QC fit into the DVD creation process?
What does “digital” mean?
What is compression?
How is something compressed?
What is bitrate?
How
does QC fit into the DVD creation process?
Quality control is crucial throughout
the DVD creation process, because the earlier that irregularities
are caught the more cost effective and precise the process
becomes.
Stages:
- Source Mastering: quality control
ensures that the digitizing of frames from film is unadulterated
- Compression: once the newly converted digital data is compressed into an MPEG-2 video and Dolby Digital audio file, 3rd i checks for irregularities.
- Emulation: at this stage, quality
control checks that the compressed movie was perfectly
combined with audio tracks and subtitles, as well as
navigation structure.
- Test Discs: having created the
initial DVD copies, 3rd i’s quality
control technicians test each one and point out any abnormalities
before they are manufactured and distributed.
Digital is the electronic method of expressing an analog event in a numeric equivalent. Visual elements within the digital domain are translated into a cluster of pixels or picture elements. Analog images or sound are recorded as waveforms. By using recording equipment that can transduce sound or light waves into voltage, and then by sampling those voltages, we arrive at a numeric equivalent of an analog value.
These values are then expressed as a binary code, composed of ones and zeros. It is a two digit language—yes and no. Each digit in this binary code is called a bit. Eight bits together make a byte, which can describe 256 distinct values, levels of brightness or color. A signal that is converted into a ten-bit number can describe over 5,000 levels of brightness or color, and sixteen-bits more than 65,000.
What is compression?Compression or encoding is the process of reducing the size of the digital video data. This ultimately becomes the heart of the DVD. A DVD is only as good as its encode. No matter how fancy your menus or navigation are, if the compression is poor the the consumer experience will be compromised.
How is something compressed?
An MPEG video compression scheme looks for similarities between frames, and averages common elements. There are several types of MPEG, the most common being MPEG-2, which is the backbone for HDTV, DVD and digital TV. It was created for the delivery of high-quality, full screen, highest-rate video. MPEG-2’s video compression method uses inter-frame compression to remove redundancy within sequential frames and creates groups of pictures (GOPs). In essence, the encoding computer compares sequential frames and looks for areas of duplication between the frames. The redundant information is noted and discarded, reducing the data size necessary to reproduce the entire frame: ‘compressing’ the image.
What is bitrate?
The term “bit-rate,” relates the amount of individual bits allocated over time to represent an audio or video element during the analog to digital conversion (sampling) process. The number of bits read or recorded in one second is the standard method of stating "bit-rate" for DVD. For example 4.5Mbps (Mega bits per second) would include 4,500,000 bits read or recorded in 1 second.